This invention relates to a process for controlling the infiltration of complex-shaped ceramic-metal composite articles and the products produced thereby.
Ceramics are typically known as low-density materials with high hardness and stiffness; however, their brittleness limits their usefulness. Furthermore, ceramics are typically formed by creating a densified compact that requires significant and expensive grinding to achieve a final shape due to the large amount of shrinkage that occurs during densification of the compact. Metals are typically non-brittle, non-breakable materials; however, they lack some of the desirable properties of the ceramics, such as high hardness and stiffness. Therefore, combining a ceramic with a metal can create a composite material that exhibits the properties of a ceramic and a metal.
Processes for making ceramic-metal composite articles using ceramic preforms are known to those skilled in the art. U.S. Pat. No. 5,308,422 discloses a process for making ceramic-metal composite articles involving forming layers of ceramic material, sintering the layers of ceramic material into a porous ceramic compact and then infiltrating the porous compact with a metal by immersing the porous body in a bath of molten metal. This process involves the uncontrolled infiltration of the metal into the ceramic compact which leads to increased finishing costs due to the regions of undesirable excess metal and phases formed on the surface(s) of the composite. An undesirable phase is a reaction phase of the chosen ceramic and metal which occurs at the infiltration interface. The reaction phase is chemically unstable or it can cause pullout damage to the surface of the infiltrated part upon machining. Pullout damage results from machining of the undesirable phase on the surface of the article with partial removal of the undesirable phase occurring which leads to pitting and defects in the surface of the article.
What is needed is a process for preparing complex-shaped ceramic-metal composite articles that require little or no finishing of the article after infiltration. What is needed is a process for controlling the infiltration of the metal into the ceramic body, such that the metal is restricted to certain regions within the article. What is needed is a process for preparing ceramic-metal composite article wherein the undesirable regions of excess metal and undesirable phases on the surface(s) are limited and controlled. What is needed is a ceramic-metal composite article wherein the undesirable regions of excess metal and undesirable phases on the surface(s) are limited and controlled.